What is the "dewpoint"?

the local t.v. weather report mentions it, but doesn't explain what it is.

4 Answers

  • 9 years ago
    Favorite Answer

    Being an old man, I will add a few things to what TQ already writes. In the past, it was not uncommon for ships to have on the side of the wheelhouse a wet and dry bulb thermometers. The wet one was kept constantly wet with cotton wool soaked in water. The idea is this: as the water evaporates, it cools down the bulb. The greater the difference between the two readings, the dryer the air is. If, for example, in the fog, no difference was registered because no evaporation occured. Plotting those temperatures was a way to predict fog, always a danger at sea.

    That wet and dry bulb instrument is also called a psychrometer and is still used today. When you have that, you use a psychrometric chart (you find then on the internet) to plot wet and dry bulb and read dew point and relative humidity.

    As the owner and pilot of a small aircraft, I always read the aviation weather report, called a METAR, where both atmospheric and dew point temperatures are written as a pair of number. The difference of which is what we call, the spread. It tells us if we risk e.g. Carburettor icing and how high the cloud ceiling can be expected.

  • Anonymous
    9 years ago

    The dew point temperature is defined as the temperature at which the air becomes saturated with water vapor when the air is cooled by removing sensible heat. It is very important in meteorology because it is directly related to the amount of water vapor in the air and it can be used to determine other variables (e.g., vapor pressure, relative humidity, wet bulb temperature, and vapor pressure deficit) that are often used in agriculture. In addition, the dew point measured during nighttime is often a good first guess for the next morning's minimum temperature. Consequently, it is extremely important for freeze protection of crops.

  • Dwight
    Lv 6
    9 years ago

    The dew point is the temperature to which the air must be cooled before it becomes saturated and water must condense out. The closer the temperature and the dew point, the more humid the air. Most often we meet humidity as "relative humidity" given as a percent - meaning the higher the percent, the closer the temperature and dew point are.

  • TQ
    Lv 7
    9 years ago

    "Dew point is the temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.

    "The dewpoint may alternatively be defined as the temperature at which the saturation vapor pressure of the parcel is equal to the actual vapor pressure of the contained water vapor.

    "The dewpoint can be measured directly by several kinds of dewpoint hygrometers or it can be deduced indirectly from psychrometers or devices that measure the water vapor density or mixing ratio."


    Source(s): Meteorologist.
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